There is a shift here to the second person. This may mean 1) the writer begins speaking to the people of Israel or 2) the writer is quoting another person speaking to the writer. (See: [[rc://en/ta/man/jit/figs-123person]])
Here "slumber" is a metaphor for "stop protecting." The negative form strengthens the statement. Alternate translation: "he will always protect you" (See: [[rc://en/ta/man/jit/figs-metaphor]] and [[rc://en/ta/man/jit/figs-doublenegatives]])